Diet and weight loss: Caloric Restriction

Caloric restriction is the most common treatment of obesity and is an essential part of any weight control program. Most quick - loss fad diets, however, stress weight loss rather than fat loss and fail to provide a regimen that can be followed for life. The goal of a dietary program should be to lose fat and then maintain the loss. Unfortunately, severe caloric restriction and the composition of these fad diets are so unpleasant and unnatural that rebound weight gains are typical.

Many of these quick - loss diets promote low carbohydrate intake, which results in dehydration as muscle and liver glycogen stores are depleted. Low carbohydrate diets lead to sodium diuresis and loss of intracellular and extracellular fluids. Although the weight loss appears impressive, most of it is in the form of water and lean mass rather than fat. Also, glycogen depletion greatly diminishes exercise capacity, which almost eliminates physical activity as a source of caloric expenditure.

The success or failure of any diet depends on its effect on energy balance. Studies of patients in metabolic wards, where diet and exercise are closely controlled and measured, have shown that people lose weight at a predictable rate when put on a low - calorie diet. Weight loss is independent of dietary composition. Fatter people tend to lose weight faster than people who are less fat. Men lose weight faster than women because of a higher lean body mass.

Although caloric content of the diet is most important for losing weight, dietary composition has an indirect influence on the quality of the weight loss. Protein (lean mass) loss is less in people consuming a high - carbohydrate diet.

Studies in metabolic wards have also shown that anyone consuming 1200 kcal per day will lose weight. They also show that water and protein loss are common during the early stages of the diet. These losses are most pronounced in more obese subjects. Exercise can slow the loss of lean
mass in obese people but cannot completely eliminate it.

Extremely low calorie diets ( <200 to 800 kcal per day) can be dangerous. Many people have died from cardiac arrest while on these diets.

Extremely low calorie diets have been associated with serious cardiac arrhythmias, loss of lean body mass, loss of hair, thinning of the skin, coldness in the extremities, gallbladder stones, gout, and elevated cholesterol. Such diets seldom result in the behavior changes necessary for permanent weight loss.
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